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2009, Vol.19, No.5

  • 1.

    Crystal growth from melt in combined heater-magnet modules

    P. Rudolph | M.Czupalla | N. Dropka and 7other persons | 2009, 19(5) | pp.215~222 | number of Cited : 0
    Abstract PDF
    Many concepts of external magnetic field applications in crystal growth processes have been developed to control melt convection, impurity content and growing interface shape. Especially, travelling magnetic fields (TMF) are of certain advantages. However, strong shielding effects appear when the TMF coils are placed outside the growth vessel. To achieve a solution of industrial relevance within the framework of the KRISTMAG ® project inner heater-magnet modules (HMM) for simultaneous generation of temperature and magnetic field have been developed. At the same time, as the temperature is controlled as usual, e.g. by DC, the characteristics of the magnetic field can be adjusted via frequency, phase shift of the alternating current (AC) and by changing the amplitude via the AC/DC ratio. Global modelling and dummy measurements were used to optimize and validate the HMM configuration and process parameters. GaAs and Ge single crystals with improved parameters were grown in HMM-equipped industrial liquid encapsulated Czochralski (LEC) puller and commercial vertical gradient freeze (VGF) furnace, respectively. The vapour pressure controlled Czochralski (VCz) variant without boric oxide encapsulation was used to study the movement of floating particles by the TMF-driven vortices.
  • 2.

    Morphological changes of BaCO3 microcrystal with the synthetic conditions

    최은지 | Young Duk Huh | 2009, 19(5) | pp.223~227 | number of Cited : 0
    Abstract PDF
    BaCO3 crystals with various morphology were prepared using precipitation, hydrothermal and ligand-assisted methods. An irregular structure of BaCO3 microparticle was obtained by simple precipitation method from Ba(NO3)2 and Na2CO3 in aqueous solution. Hexagonal pyramidals of BaCO3 were synthesized using a hydrothermal method between Ba(NO3)2 and urea. Hexagonal rods of BaCO3 were also synthesized using the ligand-assisted hydrothermal method. The aspect ratio of BaCO3 hexagonal rods was increased with the concentration of ligand.
  • 3.

    Crystal growth studies of SF6 clathrate hydrate

    이윤석 | 이주동 | Seog-Young Yoon and 6other persons | 2009, 19(5) | pp.228~236 | number of Cited : 1
    Abstract PDF
    In this study, we investigated morphological characteristics of SF6 clathrate hydrate crystals to understand its formation and growth mechanism. SF6 clathrate hydrate crystals were formed in high-pressure reaction cell charged with pure water and SF6 gas at constant pressure and temperature. Two-phase (SF6 gas/aqueous solution) and three-phase (SF6 gas/aqueous solution/SF6 liquid) conditions were investigated. In both conditions, dendritic shape hydrate crystals were grown as like fibriform crystals along upward growth direction at the gas/aqueous solution interface. In the case of the reaction process of three-phase condition, when the SF6 gas bubbles which were generated in SF6 liquid phase due to the reduction of reaction cell pressure stuck to the gas/aqueous interfaces, the hydrate phase were appeared at the surface of the bubbles. This paper presents the detail growth characteristics of SF6 hydrate crystals including crystal nucleation, migration, growth and interference.
  • 4.

    Self diffusion of cation in yttria stabilized zirconia single crystal

    정덕수 | 2009, 19(5) | pp.237~241 | number of Cited : 0
    Abstract PDF
    Dislocation dipoles were formed in the early stage of deformation of Y-CSZ single crystal at high temperatures. And the dipoles were pinched off to break into dipoles loops by dislocation climb. Dislocation loop annealing was peformed in Y-CSZ single crystal to evaluate the diffusivity of cation which was the rate-controlling ion.
  • 5.

    A study on the growth morphology of AlN crystals grown by a sublimation process

    Kang, Seung-Min | 2009, 19(5) | pp.242~245 | number of Cited : 2
    Abstract PDF
    AlN crystals were grown by a sublimation process without seed crystals and the growth morphology of them was characterized. The grown AlN crystals were a polycrystalline phase, which had a diameter of 60~200 μm and were grown with a growth rate of 0.2~0.5 μm/hr. It was observed that the as-grown crystals had a hexagonal crystal structure and revealed that these crystals were grown with a morphology of columnar morphology in the initial stage of the growth before they were enlarged in a way of a lateral growth behavior in the final stage. On the surface, a lot of pinholes were observed on the surface of crystals grown. The evolution of a growth morphology was characterized by optical and scanning electron microscopic observation
  • 6.

    A study on the Ni formation by reduction of NiO nano crystals

    Kim Chang Sam | Kang, Seung-Min | 2009, 19(5) | pp.246~250 | number of Cited : 1
    Abstract PDF
    The Ni formation behavior from the reduction of NiO nano crystals in the H2/N2 gas mixtures. The NiO nano crystals were synthesized by heat-treating nickel nitrate(Ni(NO3)2·6H2O) in the air at 500℃, and had an octahedral shape and the particle size of 200~500 nm. The NiO nano-crystals had well-developed (111) planes which is hardly formed in normal synthetic conditions. The reduction process was carried out at 300 and 600℃ for 15 and 60 minutes, respectively. When the NiO nano-crystals were reduced at 300℃, the Ni particles sustained the same octahedral shape as NiO, while Ni particles were to agglomerate at 600℃.
  • 7.

    Dispersion of nanosized noble metals in TiO2 matrix and their photoelectrode properties

    윤종원 | 2009, 19(5) | pp.251~255 | number of Cited : 0
    Abstract PDF
    Nanocomposites based on coupling TiO2 matrix with nanosized noble metals (Pt,Au) particles exhibited promising photoelectrode properties. The M/TiO2 (M = Pt,Au) nanocomposite thin films were deposited on quartz and ITO glass substrates using a co-sputtering method. TiO2 in rutile form is the dominant crystalline phase for as-deposited nanocomposite films. Along with heat treatment up to 600℃, XRD peaks of the rutile phase as well as those of noble metal increased in intensity and decreased in width, indicating the growth of crystallites. The anodic photocurrents of M/TiO2 (M = Au,Pt) thin films were observed not only in the UV range but also in the visible light range. The photocurrent of the nanocomposite films extended to the visible light region by dispersion of nano-sized noble metal in the TiO2 matrix.
  • 8.

    Properties of TiO2 thin film coated on SnO2 thin films by sol-gel method

    Tae-Young Lim | Jinho Kim | 황종회 and 2other persons | 2009, 19(5) | pp.256~261 | number of Cited : 1
    Abstract PDF
    Hydrophilic and transparent TiO2 thin film was fabricated by sol-gel method and the properties of contact angle, surface morphology, and transmittance were measured. In addition, surfactant Tween 80 was used for increasing the hydrophilic property of thin film. When the contents of Tween 80 in TiO2 solution was 0, 10, 30, 50 wt%, the contact angles of TiO2 thin film were 41.4 o , 18.2 o , 16.0 o , 13.2 o , respectively. Fabricated TiO2 thin film showed the photocatalytic property that decomposed methylene blue and decreased the absorbance of solution after UV irradiation. TiO2 thin films fabricated with the solution of 30 wt% Tween 80 were deposited on glass (bare), antimony tin oxide (ATO), fluorine tin oxide (FTO), indium tin oxide (ITO) coated glass substrates, and the contact angle and transmittance of thin film was measured. The contact angles of thin films deposited on four substrates were 16.2~27.1 o and was decreased to the range of 13.2~17.6 o after UV irradiation. Especially, the thin films coated on ATO and FTO glass substrate showed high transmittance of 74.6 % and 76.8 % in visible range, respectively, and low transmittance of 54.2 % and 40.4 % in infrared range, respectively.
  • 9.

    Fabrication of superhydrophobic TiO2 thin films by wet process

    Jinho Kim | Tae-Young Lim | Duckkyun Choi and 4other persons | 2009, 19(5) | pp.262~267 | number of Cited : 1
    Abstract PDF
    Superhydrophobic TiO2 thin films were successfully fabricated on a glass substrate by wet process. Layer-bylayer (LBL) deposition and liquid phase deposition (LPD) methods were used to fabricate the thin films of micro-nano complex structure with a high roughness. To fabricate superhydrophobic TiO2 thin films, the (PAH/PAA) thin films were assembled on a glass substrate by LBL method and then TiO2 nanoparticles were deposited on the surface of (PAH/PAA) thin film by LPD method. Subsequently, hydrophobic treatment using fluoroalkyltrimethoxysilane (FAS) was carried out on the surface of prepared TiO2 thin films. The TiO2 thin film fabricated with 45 minutes immersion time on (PAH/PAA)10 showed the RMS roughness of 65.6 nm, water contact angel of 155 o and high transmittance of above 80 % (> 650 nm in wavelength) after the hydrophobic treatment. The Surface morphologies, optical properties and contact angel of prepared thin films with different experimental conditions were measured by field emission scanning electron microscope (FE-SEM), atomic force microscope (AFM), UV-Vis spectrophotometer and contact angle meter.
  • 10.

    Preparation of Fe-AC/TiO2 composites and pH dependence of their photocatalytic activity for methylene blue

    Ze-Da Meng | Kan Zhang | Oh Won Chun | 2009, 19(5) | pp.268~276 | number of Cited : 2
    Abstract PDF
    In this study, activated carbon (AC) was treated with ferric ion by a sol-gel method. The compound (Fe-AC) was employed for the preparation of Fe-activated carbon/TiO2 (Fe-AC/TiO2) composites. The prepared Fe-AC/TiO2 composites were characterized with surface properties, structural crystallinity, elemental identification and photocatalytic activity. The SEM results showed that ferric compounds and titanium dioxide were fixed onto the AC surfaces. The XRD results showed that Fe-AC/TiO2 composites mostly contained anatase phase. EDX showed the presence of C, O, and Ti with Fe peaks in all samples. Its photocatalytic degradation effect was evaluated with the degradation behavior of the methylene blue (MB) solution. MB degradation could be attributed to the synergetic effects of adsorption, photo-degradation of TiO2 and photo-Fenton of Fe component. The degradation rate for this photocatalysis was evaluated as a function of the concentration of the dye, the amount of TiO2 and the pH. Photocataytic activity is good at activity pH.